ok i hadnt changed plugs in a while so i did those to get rid of the thought that my plugs were bad. the other day i noticed the car is stumbling on reg highway driving you know just cruisin and I even began to notice it in all gears just is more noticable cruizin in like 4th , also is it better to have the 550cc injectors as your secondaries I have a n/a car and its been street /race ported and I have massive flow thru my car .Think I need the bigger injectors or not ?main problem the stumbling at cruz :lil i ran the gas tank lower than i ran it in a long time,you know when the yellow light comes on for a while ooops...... think its the fuel filter ?

 

Could be dirty injecotrs or dirty fuel filter...when I had this same problem I replaced the fuel filter, spark plugs, wires, ran injector cleaner and non of that worked. I added a ground wire from the negative battery terminal to my chassis and that solved my problem. The factory grounds suck, and after 3800rpms our secondaries kick in. If your grounds are bad they will hesitate to kick in, and can cause a stumble even after they've kicked in.

 

Consider this just gossip. I read somewhere that the larger injectors should be put in the secondary only. They were talking about a N/A with out mods, I think. On my 87n/a I have 550's and it runs just great especially on the top end. Have mazdatrix duals from front to rear and K and N.Thats all. I think it can use some 680's. They are on the way. Either Mazdatrix or Racing Beat were recommending the 680's in the secondaries.